With the high integration of semiconductor device, the scaling down of wiring has been in progress. To that end, it is needed that an interlayer dielectric film has a low permittivity to suppress wiring delay. A SiO2 film, conventionally employed as an interlayer dielectric film, has a dielectric constant of about 4.0 which is not considered to be sufficiently low. Accordingly, various low-permittivity films have been tested and an SiCOH film having a dielectric constant of about 3.2 has been known as one of the candidates under consideration.
As shown in FIG. 13, the SiCOH film is formed by mainly introducing a CH3 group as an organic component into the SiO2 film. The SiCOH film is formed by using, e.g., a silane-based gas having a methyl group as a source material. Due to the introduction of the organic component, a film density of the SiCOH film gets lowered and, accordingly, the dielectric constant of the SiCOH film becomes lowered, too.
Further, to form a groove for burying the wiring or a connection hole in an interlayer dielectric film, a plasma etching is performed on the interlayer dielectric film and then ashing of a photoresist mask is performed. Since, however, the SiCOH film has a small film density, the SiCOH film is easily damaged by the plasma. Further, if the SiCOH film is exposed to the plasma, an organic substance is released from the SiCOH film.
To lower the permittivity of the SiCOH film, it is needed to increase a content ratio of an organic substance in the SiCOH film, for example. However, if the content ratio of the organic substance is increased, the plasma resistance of the SiCOH film gets lowered and the SiCOH film can be more easily damaged by the plasma. Further, if the SiCOH film contains a large amount of organic component, film strength of the SiCOH film gets lowered. As such, in the SiCOH film, lowering the permittivity and the plasma resistance (or the mechanical strength) are in a trade-off relationship. Accordingly, it is needed to develop an interlayer dielectric film having a low dielectric constant as well as a high plasma resistance and mechanical strength.
Japanese Patent Application Publication No. 2000-269208 (especially, paragraph Nos. 0022 and 0023) has disclosed a technique for forming an organic silica film containing a phenyl group at a low temperature by a thermal chemical vapor deposition (CVD) with bisdimethyl-amino-diphenyl-silane as a source gas and then removing the phenyl group from the film, wherein areas containing the phenyl group become hollowed out to have high porosity. Accordingly, it is possible to obtain a porous film having a low dielectric constant. Since, however, the source gas contains nitrogen, the dielectric constant is increased if the nitrogen remains in the film. In other words, it is difficult to obtain the interlayer dielectric film having a low dielectric constant while preserving a high plasma resistance and mechanical strength by the technique of Japanese Patent Application Publication No. 2000-269208.